The Space Infrared Telescope Facility (SIRTF) was successfully launched on August 25, 2003. SIRTF is an observatory for infrared astronomy from space. It has an 85cm diameter beryllium telescope operating at 5.5 K and a projected cryogenic lifetime of 4 to 6 years based on early flight performance. SIRTF has completed its in-orbit checkout and has become the first mission to execute astronomical observations from a solar orbit. SIRTF's three instruments with state of the art detector arrays provide imaging, photometry, and spectroscopy over the 3-180 micron wavelength range. SIRTF is achieving major advances in the study of astrophysical phenomena from the solar system to the edge of the Universe. SIRTF completes NASA's family of Great Observatories and serves as a cornerstone of the Origins program. Over 75% of the observing time will be awarded to the general scientific community through the usual proposal and peer review cycle. SIRTF has demonstrated major advances in technology areas critical to future infrared missions. These include lightweight cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiative and cryogenic cooling, which allows a telescope to be launched warm and to be cooled in space. These thermal advances are enabled by the use of an Earth-trailing solar orbit which will carry SIRTF to a distance of ~0.6 AU from Earth in 5 years. The SIRTF project is managed for NASA by the Jet Propulsion Laboratory which employs a novel JPL-industry team management approach. This paper provides an overview of the SIRTF mission, telescope, cryostat, instruments, spacecraft, orbit, operations and project management approach; and this paper serves as an introduction to the accompanying set of detailed papers about specific aspects of SIRTF.

The Cryogenic Telescope Assembly (CTA) on the Spitzer Space Telescope employs a revolutionary warm launch design. Unlike previous space cryogenic telescopes, the Spitzer telescope is mounted outside of the cryostat and was launched at ambient temperature. The telescope was cooled through a combination of passive radiation and controlled vapor cooling from the superfluid helium cryostat. Launched in August 2003 with 49 kg of helium, the 0.85-meter telescope cooled to below 5.5 K within the initial 45 days of flight in accordance with analytical predictions. Despite an aggressive schedule of instrument initialization and checkout testing during the first two months of flight, the CTA met the temperature requirements for all checkout activities. The transient flight performance of this multi-stage thermal/cryogenic system has been found to agree well with pre-launch predictions over the broad temperature range. With an emphasis on early flight cool-down behavior, this report highlights the pre-launch cryostat preparation, the thermal behavior during cryostat blow-down, comparisons to pre- and post-launch model predictions, and in-flight helium mass measurement. The post cool down performance and rate of helium use is also discussed.

The Spitzer Space Telescope (formally known as SIRTF) was successfully launched on August 25, 2003, and has completed its initial in-orbit checkout and science validation and calibration period. The measured performance of the observatory has met or exceeded all of its high-level requirements, it entered normal operations in January 2004, and is returning high-quality science data. A superfluid-helium cooled 85 cm diameter telescope provides extremely low infrared backgrounds and feeds three science instruments covering wavelengths ranging from 3.6 to 160 microns. The telescope optical quality is excellent, providing diffraction-limited performance down to wavelengths below 6.5 microns. Based on the first helium mass and boil-off rate measurements, a cryogenic lifetime in excess of 5 years is expected. This presentation will provide a summary of the overall performance of the observatory, with an emphasis on those performance parameters that have the greatest impact on its ultimate science return.

The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center.

The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.

We present the on-orbit performance results of the Pointing Calibration and Reference Sensor (PCRS) for the Spitzer Space Telescope. A cryogenic optical (center wavelength 0.55 um) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from Spitzer's star tracker and gyroscopes to obtain the actual pointing of the Spitzer telescope. The PCRS calibrates out thermomechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. By using only 16 pixels, the PCRS provides high precision centroiding with extremely low (~64 uW) power dissipation, resulting in minimal impact to Spitzer's helium lifetime. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-s radial, which represents ~1/100 pixel centroiding. The Spitzer Space Telescope was launched on 25 August, 2003 and completed its In-Orbit Checkout phase two months later; the PCRS has been operating failure-free ever since.

Wide Field Camera 3 (WFC3) is a panchromatic UV/visible/near-infrared camera whose development is currently nearing completion, for a planned installation into the Hubble Space Telescope. WFC3 provides two imaging channels. The UVIS channel features a 4096 × 4096 pixel CCD focal plane with sensitivity from 200 to 1000 nm and a 160 × 160 arcsec field of view. The UVIS channel provides unprecedented sensitivity and field of view in the near ultraviolet for HST. The IR channel features a 1014 × 1014 pixel HgCdTe focal plane covering 800 to 1700 nm with a 139 × 123 arcsec field of view, providing a substantial advance in IR survey efficiency for HST. The construction of WFC3 is nearly complete, and the instrument is well into its integration and test program. At the time of this writing (July 2004) the manned HST Servicing Mission 4 that was intended to install WFC3 and other hardware has been cancelled, but a robotic servicing possibility is under intensive investigation. We present the current status and performance of the instrument and also describe some aspects of WFC3 that are relevant to a robotic installation.

Temperature variations in the NICMOS detectors arise from a variety of
thermal sources. These thermal variations lead to several image
artifacts which must be removed before making quantitative scientific
measurements from NICMOS data. Future instruments would do well to
minimize sources of thermal instabilities in their detectors. A related problem is the inability to directly measure detector temperature from bias due to the instability of the low-voltage power supply in NICMOS. Identifying ways to directly monitor detector temperatures would be an important benefit for future missions.

ASTRO-F is the Japanese infrared astronomical satellite. The mission purpose is the infrared sky survey with much higher sensitivities and spatial resolutions than those of the previous survey mission IRAS. The ASTRO-F has a liquid-helium cooled telescope with an aperture of 68.5 cm. The lightweight liquid helium cryostat has been developed for the ASTRO-F. The use of cryocoolers and other design features will realize the cryogen life of 550 days in orbit with only 170-liter liquid helium. The attitude control system provides capabilities of a continuous sky survey and also pointing observations. The absolute accuracy of the attitude control is approximately 10 arcsec, and the stability is better than 1 arcsec. The astronomical data will be sent to the ground in the rate of 4 Mbps through the X-band link. The telemetry data amount to more than 2 GB per day. The planned launch date was February 2004, but it has delayed because of a failure in the mirror support mechanism of the telescope system. Though the new launch date has not been decided formally, the launch in 2005 summer is now targeted.

The Infrared Camera (IRC) is one of the focal-plane instruments on board the Japanese infrared astronomical space mission ASTRO-F. It will make wide-field deep imaging and low-resolution spectroscopic observations over a wide spectral range in the near- to mid-infrared (2-26um) in the pointed observation mode of the ASTRO-F. The IRC will also be operated in the survey mode and make an all-sky survey at mid-infrared wavelengths. It comprises three channels. The NIR channel (2-5um) employs a 512x412 InSb array, whereas both the MIR-S (5-12um) and the MIR-L (12-26um) channels use 256x256 Si:As impurity band conduction (IBC) arrays. The three channels will be operated simultaneously. All the channels have 10'x10' fields of view with nearly diffraction-limited spatial resolutions. The NIR and MIR-S share the same field of view, while the MIR-L will observe the sky about 25' away from the NIR/MIR-S field of view. The IRC will give us deep insights into the formation and evolution of galaxies, the properties of brown dwarfs, the evolution of planetary disks, the process of star-formation, the properties of the interstellar medium under various physical environments, as well as the nature and evolution of solar system objects. This paper summarizes the latest laboratory measurements as well as the expected performance of the IRC.

An all-sky survey in two mid-infrared bands which cover wavelengths of 5-12um and 12-26μm with a spatial resolution of ~9" is planned to be performed with the Infrared Camera (IRC) on board the ASTRO-F infrared astronomical satellite. The expected detection limits for point sources are few tens mJy. The all-sky survey will provide the data with sensitivities more than one order of magnitude deeper and with spatial resolutions an order of magnitude higher than the Infrared Astronomical Satellite (IRAS) survey.
The IRC is optimally designed for deep imaging in pointing observations. It employs 256x256 Si:As IBC infrared focal plane arrays (FPA) for the two mid-infrared channels. In order to make observations with the IRC during the survey mode of the ASTRO-F, a new operation method for the arrays has been developed - the scan mode operation. In the scan mode, only 256 pixels in a single row aligned in the cross-scan direction on the array are used as the scan detector and sampled every 44ms. Special cares have been made to stabilize the temperature of the array in the scan mode, which enables to achieve a low readout noise compatible with the imaging mode (~30 e-). The flux calibration method in the scan mode observation is also investigated. The performance of scan mode observations has been examined in computer simulations as well as
in laboratory simulations by using the flight model camera and moving artificial point sources. In this paper we present the scan mode operation method of the array, the results of laboratory performance tests, the results of the computer simulation, and the expected performance of the IRC all-sky survey observations.

The Far-Infrared Surveyor (FIS) is a focal plane instrument of the ASTRO-F satellite, and is designed primarily to achieve far-infrared all sky survey with four photometric bands in wavelength range of 50 - 200um. Compared to IRAS, the FIS has higher sensitivity, higher spatial resolution, and longer wavelength coverage. The FIS also has spectroscopic capability with a Fourier transform spectrometer (FTS). In order to assemble these two kinds of instrument into a small and light body, we have developed new compact detector arrays and adopt the unique optical design. In the first half year of the ASTRO-F mission, the all sky survey is performed intensively, and is completed in the following half year. In addition to this survey, the telescope can be kept to a specific direction during 10 minutes for pointing observations. In pointing observations, we can take deep photometric images by using the photometric mode, or can take spectra by using the FTS. According to the laboratory calibration, it is expected that the detection limit of the all sky survey is almost one order of magnitude better than the IRAS one. The FTS could take spectra with full spectral resolution for about two orders of magnitude brighter sources than the detection limit of the all sky survey for one pointing observation. Due to the imaging FTS, the observing efficiency is much improved for the extended sources. The FIS will provide us unique and valuable observational data in the far-infrared wavelength region.

Herschel is the fourth cornerstone mission in the European Space Agency (ESA) science programme. It will perform imaging photometry and spectroscopy in the far infrared and submillimetre part of the spectrum, covering approximately the 57-670 μm range. The key science objectives emphasize current questions connected to the formation of galaxies and stars, however, having unique capabilities in several ways, Herschel will be a facility available to the entire astronomical community. Herschel will be equipped with a 3.5 metre diameter passively cooled telescope. The science payload complement - two cameras/medium resolution spectrometers (PACS and SPIRE) and a very high resolution heterodyne spectrometer (HIFI) - will be housed in a superfluid helium cryostat. The ground segment will be jointly developed by the ESA, the three instrument teams, and NASA/IPAC. Herschel is scheduled to be launched into a transfer trajectory towards its operational orbit around the Earth-Sun L2 point by an Ariane 5 (shared with the ESA cosmic background mapping mission Planck) in 2007. Once operational Herschel will offer a minimum of 3 years of routine observations; roughly 2/3 of the available observing time is open to the general astronomical community through a standard competitive proposal procedure.

SPIRE, the Spectral and Photometric Imaging Receiver, is one of three scientific instruments which will fly on the European Space Agency's Herschel Space Observatory. SPIRE contains two sub-instruments: a three-band imaging photometer operating at 250, 360 and 520 microns, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 microns. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 300 mK. The photometer field of view of is 4 x 8 arcminutes, observed simultaneously in the three spectral bands. An internal beam steering mirror allows spatial modulation of the telescope beam and will be used to jiggle the field of view in order to produce fully-sampled images. Observations can also be made by scanning the telescope without chopping. The FTS has an approximately circular field of view with a diameter of 2.6 arcminutes, and employs a dual-beam configuration with broad-band intensity beam dividers to provide high efficiency and separated output and input ports. The spectral resolution can be adjusted between 0.04 and 2 cm-1 (λ/Δλ = 20 - 1000 at 250 microns). The instrument design, operating modes, and estimated sensitivity are described, and the current status of the project is reported.

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments for ESA's far infrared and submillimetre observatory, Herschel. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 x 25 pixels, each, and two filled Si bolometer arrays with 16 x 32 and 32 x 64 pixels, respectively, to perform imaging line spectroscopy and imaging photometry in the 57-210 micron wavelength band. In photometry mode, it will simultaneously image two bands, 60-85 micron or 85-130 micron and 130-210 micron, over a field of view of ~ 1.75'x3.5', with full beam sampling in each band. In spectroscopy mode, it will image a field of ~ 50"x50", resolved into 5 x 5 pixels, with an instantaneous spectral coverage of ~ 1500 km/s and a spectral resolution of ~ 75 - 300 km/s. In both modes background-noise limited peformance is expected, with sensitivities (5σ in 1h) of ~3 mJy or 3-10x10-18 W/m2, respectively.

The future ESA space mission Planck Surveyor mission will measure the Cosmic Microwave Background temperature and polarisation anisotropies in a frequency domain comprised between 30GHz and 1THz. On board two instruments, LFI based on HEMT technology and HFI using bolometric detectors. We present the optical solutions adopted for this mission, in particular the focal plane design of HFI, concept which has been applied already to other instruments such as the balloon borne experiment Archeops.

PLANCK represents the third generation of mm-wave instruments designed for space observations of Cosmic Microwave Background anisotropies within the new Cosmic Vision 2020 ESA Science Programme. The PLANCK survey will cover the whole sky with unprecedented sensitivity, angular resolution, and frequency coverage. The expected scientific return will be enormous, both for the cosmological constraints that will be set and for the gold mine of information contained in the astrophysical foregrounds. To reach these ambitious scientific goals, the control of systematic effects is mandatory and a careful instrument design is needed, as well as an accurate knowledge of instrumental characteristics. The Low Frequency Instrument (LFI), operating in the 30 ÷ 70 GHz range, is one of the two instruments onboard PLANCK Satellite, sharing the focal region of a 1.5 meter off-axis dual reflector telescope together with the High Frequency Instrument (HFI) operating at 100 ÷ 857 GHz. We present a detailed study carried out by the LFI team on the performances of the PLANCK telescope coupled with LFI feed horns, both in the main beam and in the sidelobe region.

The JWST project at the GSFC is responsible for the development, launch, operations and science data processing for the James Webb Space Telescope. The JWST project is currently in phase B with its launch scheduled for August 2011. The project is a partnership between NASA, ESA and CSA. The U.S. JWST team is now fully in place with the recent selection of Northrop Grumman Space Technology (NGST) as the prime contractor for the telescope and the Space Telescope Science Institute (STScI) as the mission operations and science data processing lead. This paper will provide an overview of the current JWST architecture and mission status including technology developments and risks.

The scientific requirements of the James Webb Space Telescope fall into four themes. The End of the Dark Ages: First Light and Reionization seeks to identify the first luminous sources to form and to determine the ionization history of the Universe. The Assembly of Galaxies seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present. The Birth of Stars and Protoplanetary Systems seeks to unravel the birth and early evolution of stars, from infall onto dust-enshrouded protostars, to the genesis of planetary systems. Planetary Systems and the Origins of Life seeks to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for life in those systems. These themes will guide the design and construction of the observatory.

JWST will be used to help understand the shape and chemical composition of the universe, and the evolution of galaxies, stars and planets. With a 6.5 meter primary mirror, the Observatory will observe red shifted light from the early history of the universe, and will see objects 400 times fainter than those seen from large ground-based telescopes or the current generation of space-based infrared telescopes. NASA Goddard Space Flight Center (GSFC) manages JWST with contributions from a number of academic, government, and industrial partners. The contract to build the space-based Observatory for JWST was awarded to the Northrop Grumman Space Technology (NGST)/Ball/Kodak/ATK team.

The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope and to the Spitzer Space Facility, will yield astounding breakthroughs in the realms of infrared space science. The science instrument suite for this Observatory will consist of a Near-Infrared Camera, a Near-Infrared Spectrograph, a Mid-Infrared Instrument with imager, coronagraph and integral field spectroscopy modes, and a Fine Guider System Instrument with both a Guider module and a Tunable Filter Module. In this paper we present an overview of the optical designs of the telescope and instruments.

The NIRCam science objectives are the detection and identification of "first light" objects, the study of star and brown dwarf formation, and the detection and characterization of planetary systems and their formation. These three science programs are also the key objectives of the JWST program as a whole. The NIRCam instrument design is optimized for these objectives within the mission constraints. NIRCam consists of two optics modules, each with a field of view of 2.2 arcmin square. The modules are identical except for the mechanical layout. Each module consists of two channels divided by a dichroic beamsplitter. The short wavelength channel has a band pass of 0.6 - 2.3 microns, with pixels sized for Nyquist sampling of the PSF at 2.0 microns. The long wavelength channel has a band pass of 2.4 - 5.0 microns, with pixels sized for Nyquist sampling at 4.0 microns. Selections of wide (R~4), intermediate (R~10), and narrow (R~100) bandwidth filters are provided in each of the four channels, along with coronagraphic occulting masks and pupil stops. A refractive optical design results in a smaller instrument volume and mass, provides good images at the pupils for wavefront sensing and coronagraphy, allows good access to the pupils and focal planes, and relaxes the alignment requirements compared to a reflective design. The NIRCam instrument is funded by NASA/GSFC under contract NAS5-02105.

The James Webb Space Telescope (JWST) will be equipped with a Near Infrared Multi-Object Spectrograph (NIRSpec), in order to record simultaneously several hundred spectra in a single observation run. The selection of the objects in the field of view will be done by a micro-elecro-mechanical system (MEMS): a micro-shutter array. This
array is easily reconfigurable and can generate any slit mask geometry. At the Laboratoire d’Astrophysique de Marseille, we have developed since several years different tools for the modeling and the characterization of these MOEMS slit masks. Our model, based on Fourier theory, addresses two key parameters for the MOS performance: contrast and spectral photometric variation (SPV). The integration in a single model of the JWST telescope, the micro-shutter slit mask, the
spectrograph and the detector is proposed. The JWST telescope simulator assess pupil shape with low, mid and high frequencies aberrations on the whole telescope as well as on each segment. Additional wavefront aberrations generated by the fore-optics and the spectrograph are also taken into account. NIRSpec performance is then calculated as function of multiple parameters such as telescope pupil shear, object position in the field, plate scale, object location within the slit, pupil oversizing, wavelength, and dithering strategy. Evaluation of the encircled energy is also presented, including the spectrograph aberrations.

The Near Infrared Spectrograph (NIRSpec) for the James Webb Space Telescope (JWST) is a multi-object spectrograph operating in the 0.6-5.0 μm spectral range. One of the primary scientific objectives of this instrument is to measure the number and density evolution of galaxies following the epoch of initial formation. NIRSpec is designed to allow simultaneous observation of a large number of sources, vastly increasing the capability of JWST to carry out its objectives. A critical element of the instrument is the programmable field selector, the Microshutter Array. The system consists of four 175 x 384 close packed arrays of individually operable shutters, each element subtending 0.2” x 0.4”on the sky. This device allows simultaneous selection of over 200 candidates for study over the 3.6’ x 3.6’ field of the NIRSpec, dramatically increasing its efficiency for a wide range of investigations. Here, we describe the development, production, and test of this critical element of the NIRSpec.

The MIRI is the mid-IR instrument for JWST and provides imaging, coronography and low and medium resolution spectroscopy over the 5-28μm band. In this paper we provide an overview of the key driving requirements and design status.

The science instrumentation for the James Webb Space Telescope (JWST) has concluded its Phase A definition stage. We have developed a concept for the JWST Fine Guidance Sensor (FGS), which will form the Canadian contribution to the mission. As part of the JWST re-plan in early 2003, the FGS design was recast to incorporate a narrow-band (R~100) science-imaging mode. This capability was previously resident in the NIRCam instrument. This FGS science mode makes use of tunable filters and filter wheels containing blocking filters, calibration sources and aperture masks. The science function of the FGS Tunable Filters (FGS-TF) remains complementary to the NIRCam science goals. Narrow-band FGS-TF imaging will be employed during many of the JWST deep imaging surveys to take advantage of the sensitivity to emission line objects. The FGS-TF will also provide a coronagraphic capability for the characterization of host galaxies of active galactic nuclei and for the characterization of extra solar planets. The primary function of the FGS remains to provide the sensor data for the JWST Observatory line-of-sight stabilization system. We report here on the overall configuration of the FGS and we indicate how the concept meets the performance and interface requirements.

The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) is a segmented, cryogenic telescope scheduled for launch in 2011. In September of 2002, NASA selected prime contractor Northrop Grumman Space Technology (NGST) to build the observatory including management of the OTE. NGST is teamed with subcontractors Ball Aerospace, Alliant Techsystems (ATK), and Kodak. The team has completed several significant design, technology, architecture definition, and manufacturing milestones in the past year that are summarized in this paper.

The James Webb Space Telescope (JWST) conducted a phased down select for its primary mirror. Using the results of the Advanced Mirror System Demonstrator (AMSD) as a basis, the Mirror Recommendation Board (MRB) assessed the suitability for JWST of candidate mirrors in the areas of performance, schedule, cost and risk. Beryllium was selected for the JWST primary mirror. This paper summarizes the evaluation and selection process.

The 1.4-meter semi-rigid, beryllium Advanced Mirror System Demonstrator (AMSD) mirror completed initial cryogenic testing at Marshall’s X-ray Calibration Facility (XRCF) in August of 2003. Results of this testing show the mirror to have very low cryogenic surface deformation and possess exceptional figure stability. Additionally, the mirror substrate exhibits virtually no change in surface figure over the James Webb Space Telescope (JWST) operational temperature range of 30 to 62 Kelvin. The lightweighted, semi-rigid mirror architecture approach demonstrated here is a precursor to the mirror technology being applied to the JWST observatory. Testing at ambient and cryogenic temperatures included the radius of curvature actuation system and the rigid body displacement system. These two systems incorporated the use of 4 actuators to allow the mirror to change piston, tilt, and radius of curvature. Presented here are the results of the figure change, alignment change, and radius change as a function of temperature. Also shown will be the actuator influence functions at both ambient and cryogenic temperatures.

The Northrup-Grummann/Ball/Kodak team is building the James Webb Space Telescope (JWST), scheduled for launch in 2011. Part of Ball’s responsibility is to develop the wavefront sensing and control (WFS&C) algorithms and software that will be used to provide the level of imaging performance needed to support the mission’s science objectives. Wavefront sensing on JWST differs from that performed on many ground-based telescopes in that it is conducted entirely within the focal plane of it’s chief science camera, the Near Infrared Camera (NIRCam). In a sense, the complexity of a conventional wavefront sensor is eliminated, in favor of rather complex image processing performed on the ground, to extract the wavefront information. This paper will describe the algorithms being developed for JWST. Specifically, we will describe algorithms for the coarse alignment of the primary mirror segments and the secondary mirror, the coarse phasing of the primary mirror segments, and the fine phasing of the entire telescope. We will also present algorithms for monitoring the wavefront quality throughout the JWST mission.

Dispersed Fringe Sensing (DFS) is an efficient and robust method for coarse phasing of a segmented primary mirror such as the James Webb Space Telescope (JWST). Results from testbed experiments and modeling have shown that among the many factors that affect the performance of DFS, the diffraction from segment aperture and the interference between the segment wavefronts have the most intrinsic influence on the DFS performance. In this paper, modeling and simulations based on diffraction are used to study the formation of DFS fringe and fringe properties such as visibility. We examine the DFS piston detection process and explore the limitation of DFS wavefront piston detection accuracy and the DFS dynamic range under different segment aperture geometries, aperture orientations, and image samplings.

Stellar Imager (SI) is a potential NASA space-based UV imaging interferometer to resolve the stellar disks of nearby stars. SI would consist of 20 - 30 separate spacecraft flying in formation at the Earth-Sun L2 libration point. Onboard wavefront control would be required to initially align the formation and maintain alignment during science observations and after array reconfiguration. The Fizeau Interferometry Testbed (FIT) is a testbed currently under development at the NASA/Goddard Space Flight Center to develop and study the wavefront control methodologies for Stellar Imager and other large, sparse aperture telescope systems. FIT consists of 7 articulated spherical mirrors in a Golay pattern, expandable up to 30 elements, and reconfigurable into multiple array patterns. FIT’s purpose is to demonstrate image quality versus array configuration and to develop and advance the wavefront control for SI. FIT uses extended scene wavelength, focus and field diversity to estimate the wavefront across the set of apertures. The recovered wavefront is decomposed into the eigenmodes of the control matrix and actuators are moved to minimize the wavefront piston, tip and tilt. Each mirror’s actuators are 3 degrees of freedom, however, they do not move each of the mirrors about a point on each mirrors surface, thus the mapping from wavefront piston, tip/tilt to mirror piston, tip/tilt is not diagonal. We initially estimate this mapping but update it as part of wavefront sensing and control process using system identification techniques. We discuss the FIT testbed, wavefront control methodology, and show initial results from FIT.

Large deployable space telescopes like the James Webb Space Telescope (JWST) may have large errors after deployment that must be corrected in situ. One approach is to correct the errors successively. In this paper, we present a new approach to correct large phase aberrations during the coarse figuring stage of the initial alignment. Intensity data is obtained from multiple planes: pupil plane and additional planes in the nearfield of the pupil plane. The irradiance transport equation is used in a new manner used to estimate the phase aberrations at the pupil. The technique was demonstrated in the lab to estimate phase aberrations approaching 20 waves.

The SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a Japanese astronomical infrared satellite project with a 3.5-m telescope, is scheduled for launch in early 2010s. The telescope is cooled down to 4.5 K in space by a combination of mechanical coolers with an efficient radiative cooling system. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 µm at 4.5 K. Two candidate materials, silicon carbide (SiC) and carbon-fiber-reinforced SiC (C/SiC composite), are currently under investigation for the primary mirror. A monolithic mirror design will be adopted in both cases because of the technical feasibility and reliability. This paper reports the current design and status of the SPICA telescope together with some of our recent results on laboratory cryogenic tests for the SiC and C/SiC composite mirrors.

Placed on the L2 Lagrangian point, the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) will operate in the 5 to 200 μm wavelength range, at 4.5K. The large aperture telescope (3.5m diameter in a single piece) requires a strong manufacturing mastering, associated with high technical performances. The background acquired by EADS-Astrium (France) on the 3.5m Silicone Carbide Herschel Telescope is a key for the success of the SPICA development. EADS-Astrium has been awarded by the Japan Aerospace Exploration Agency (JAXA) and Sumitomo Heavy Industries to assess the feasibility of the 3.5m all SiC telescope through a design phase contract. The Telescope driving requirements are the large diameter of 3.5m especially critical for the manufacturing aspects, and the Wave Front Error which has to be kept below 350nm rms over a large temperature range from ambient to the operational temperature of 4.5K which requires a strong mastering of the distortions.

SiC (silicon carbide) lightweight mirrors are used for a large number of space telescopes, and SiC is also candidate as hopeful material for segmented mirrors of the next generation ground based telescopes from 30 to 100 m in diameter. However, an SiC mirror is difficult to shape because the material is very hard and brittle. We are developing an SiC mirror by means of the ELID (ELectrolytic In-process Dressing) grinding method, a grinding machine with rotary table of 800 mm in diameter and precision of 10 nm in control resolution, and computational simulations. The ELID grinding method is versatile for fabrications of very hard materials. In this study, we introduce test fabrications of SiC mirrors with 360 mm in diameter and equilateral triangle rib structures in the rear face. We developed a support tool with air actuator and oil pressure clamp for suppression of the mirror deformation for manufacturing of the thin mirror.

The technology associated with the use of silicon carbide (SiC) for high-performance mirrors has matured significantly over the past 10-20 years. More recently, the material has been considered for cryogenic applications such as space-based infrared telescopes. In light of this, NASA has funded several technology development efforts involving SiC mirrors. As part of these efforts, three lightweight SiC mirrors have been optically tested at cryogenic temperatures within the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC). The three mirrors consisted of a 0.50 m diameter carbon fiber-reinforced SiC, or C/SiC, mirror from IABG in Germany, a 0.51 m diameter SiC mirror from Xinetics, Inc., and a 0.25 m diameter SiC mirror from POCO Graphite, Inc. The surface figure error was measured interferometrically from room temperature (~290 K) to ~30 K for each mirror. The radius-of-curvature (RoC) was also measured over this range for the IABG C/SiC & Xinetics SiC mirrors. This paper will describe the test goals, the test instrumentation, and the test results for these cryogenic tests.

Many authors have endorsed the concept of assembly of large optics in space and have pointed out the technology needs for astronauts, infrastructure, robots and the observatories themselves. In this paper, we consider the technical issues associated with the integration and test in space of large optics during the next 15 years or so, when human activity is largely confined to low Earth orbit (LEO). We identify technical areas that need development and define a first version of the processes that might be used to create successful telescope missions that are tested in space. We identify a pathway that supports scalable solutions for very large systems necessary for imaging planets in other solar systems and other magnificent science. The investment in space integration and testing technology will return important dividends to designers of large space optics of the future. This approach to space optics testing is attractive because it overcomes the limits of ground testing associated with large test chambers, star simulators and the effects of gravity. It also directly benefits from, and supports, the technology and infrastructure investments about to be made by the new NASA Exploration Systems Enterprise, allowing both observatories and exploration missions to be assembled.

The National Aeronautics and Space Administration (NASA) is planning future deep space missions requiring space-based imaging reconnaissance of planets and recovery of imagery from these missions via optical communications. Both applications have similar requirements that can be met by a common aperture. The Johns Hopkins University Applied Physics Laboratory in collaboration with commercial and academic partners is developing a new approach to deploying and controlling large aperture (meter-class) optical telescopes on spacecraft that can be rapidly launched and deployed. The deployment mechanism uses flexible longeron struts to deploy the secondary. The active control system uses a fiber-coupled laser array near the focal plane that reflects four collimated laser beams off of the periphery of the secondary to four equally-disposed quad cell sensors at the periphery of the primary to correct secondary-to-primary misalignments and enable motion compensation. We describe a compensation technique that uses tip/tilt and piston actuators for quasi-static bias correction and dynamic motion compensation. We also describe preliminary optical tests using a commercial Schmidt-Cassegrain telescope in lieu of an ultra-lightweight composite Cassegrain, which is under development by Composite Mirror Applications, Inc. Finite element and ray trace modeling results for a 40 cm composite telescope design will also be described.

Inspired by a paper by Hyde (1999) (H99) we propose a 30-m diffractive Fresnel lens of ultra-high molecular-weight polyethylene (UHMW-PE) as the Primary Lens (L1) of a large cold far-IR and submillimetre space telescope. The design comprises Lens (L1) and Instrument (ISC) spacecraft 3 km apart, orbiting the Sun-Earth second Lagrangian point L2. In the Instrument S/C an off-axis Ritchey-Chretien Field Optical system (FO) re-images L1 onto a Fresnel corrector (FC). Achromatic over a bandpass λ/Δλ ~7.5 at a basic wavelength of 1.2mm and its harmonics, the design offers diffraction-limited performance from ~20 to ~700μm and a 1'x4' FOV. Positional tolerances appear to allow deployment of the lens by very simple means (we suggest using Shape Memory Alloys and pneumatic pressure). The most serious technical challenge may be material homogeneity. Behind an effective sunshade L1 should cool to ~10K by radiation to space in ~1y: its dominant heat source will be the zodiacal emission. GISMO resolves the FIR background at λ ~ 200μm: an all-sky survey to ~100μJy could in principle take <1y. GISMO should equal or outperform the 10m, 4K conceptual design for SAFIR (the Single-Aperture Far-IR and submillimetre mission, currently under study by NASA) in all observing modes and may offer a simpler (cheaper) and more capable alternative design “flavour” for this flagship future mission.

The solar optical telescope onboard the Solar-B is aimed to perform a high precision polarization measurements of the solar spectral lines in visible wavelengths to obtain, for the first time, continuous sets of high spatial resolution (~0.2arcsec) and high accuracy vector-magnetic-field map of the sun for studying the mechanisms driving the fascinating activity phenomena occurring in the solar atmosphere. The optical telescope assembly (OTA) is a diffraction limited, aplanatic Gregorian telescope with an aperture of Φ500mm. With a collimating lens unit and an active folding mirror, the OTA provides a pointing-stabilized parallel beam to the focal plane package (FPP) with a field of view of about 360x200arcsec. In this paper we identify the key technical issues of OTA for achieving the mission goal and describe the basic concepts in its optical, mechanical and thermal designs. The strategy to verify the in-orbit performance of the telescope is also discussed.

The SUNRISE balloon project is a high-resolution mission to study solar magnetic fields able to resolve the critical scale of 100 km in the solar photosphere, or about one photon mean free path. The Imaging Magnetograph eXperiment (IMaX) is one of the three instruments that will fly in the balloon and will receive light from the 1m aperture telescope of the mission. IMaX should take advantage of the 15 days of uninterrupted solar observations and the exceptional resolution to help clarifying our understanding of the
small-scale magnetic concentrations that pervade the solar surface. For this, IMaX should act as a diffraction limited imager able to carry out spectroscopic analysis with resolutions in the 50.000-100.000 range and capable to perform polarization measurements. The solutions adopted by the project to achieve all these three demanding goals are explained in this article. They include the use of Liquid Crystal Variable Retarders for the polarization modulation, one
LiNbO3 etalon in double pass and two modern CCD detectors that allow for the application of phase diversity techniques by slightly changing the focus of one of the CCDs.

NASA has decided to move forward with two complementary Terrestrial Planet Finder (TPF) missions, a visible coronagraph and an infrared formation flying interferometer in collaboration with ESA. These missions are major missions in the NASA Office of Space Science Origins Theme. The primary science objectives of the TPF missions are to search for, detect, and characterize planets and planetary systems beyond our own Solar System, including specifically Earth-like planets.

The Terrestrial Planet Finder (TPF) seeks to revolutionize our understanding of humanity's place in the universe - by searching for Earth-like planets using reflected light, or thermal emission in the mid-infrared. Direct detection implies that TPF must separate planet light from glare of the nearby star, a technical challenge which has only in recent years been recognized as surmountable. TPF will obtain a low-resolution spectra of each planet it detects, providing some of its basic physical characteristics and its main atmospheric constituents, thereby allowing us to assess the likelihood that habitable conditions exist there. NASA has decided the scientific importance of this research is so high that TPF will be pursued as two complementary space observatories: a visible-light coronagraph and a mid-infrared formation-flying interferometer. The combination of spectra from both wavebands is much more valuable than either taken separately, and it will allow a much fuller understanding of the wide diversity of planetary atmospheres that may be expected to exist. Measurements across a broad wavelength range will yield not only physical properties such as size and albedo, but will also serve as the foundations of a reliable and robust assessment of habitability and the presence of life.

One of humanity's oldest questions is whether life exists elsewhere in the universe. The Terrestrial Planet Finder (TPF) mission will survey stars in our stellar neighborhood to search for planets and perform spectroscopic measurements to identify potential biomarkers in their atmospheres. In response to the recently published President's Plan for Space Exploration, TPF has plans to launch a visible-light coronagraph in 2014, and a separated-spacecraft infrared interferometer in 2016. Substantial funding has been committed to the development of the key technologies that are required to meet these goals for launch in the next decade. Efforts underway through industry and university contracts and at JPL include a number of system and subsystem testbeds, as well as components and numerical modeling capabilities. The science, technology, and design efforts are closely coupled to ensure that requirements and capabilities will be consistent and meet the science goals.

Terrestrial Planet Finder Coronagraph, one of two potential architectures, is described. The telescope is designed to make a visible wavelength survey of the habitable zones of at least thirty stars in search of earth-like planets. The preliminary system requirements, optical parameters, mechanical and thermal design, operations scenario and predicted performance is presented. The 6-meter aperture telescope has a monolithic primary mirror, which along with the secondary tower, are being designed to meet the stringent optical tolerances of the planet-finding mission. Performance predictions include dynamic and thermal finite element analysis of the telescope optics and structure, which are used to make predictions of the optical performance of the system

The Hubble Space Telescope (HST) provides the most versatile high contrast imaging capabilities of any current telescope. It allows high resolution, high dynamic range imaging from the near-ultraviolet to the near-infrared with both direct and coronagraphic methods. Its main advantage over ground-based systems is its stable point spread function. A review of the performance of HST as a high contrast imaging system is presented, including the abilities of all of the current HST cameras. Special emphasis is placed on items that are important to future missions (e.g. the Terrestrial Planet Finder), including mid-spatial frequency wavefront stability, coronagraphic system alignment, and observing methods.

The direct detection of Earthlike planets in the visible is a very challenging goal This paper describes a new concept for visible direct detection of Earths using a nulling interferometer instrument behind a 4m telescope in space. The basic concept is described along with the key advantages of the nulling interferometer over more traditional approaches, an apodized aperture telescope or coronagraph. In the baseline design, a 4 beam nuller produces a very deep theta^4 null. With perfect optics, the stellar leakage is less than 1e-11 of the starlight at the location of the planet. With diffraction limited (lambda/20) telescope optics suppression of the starlight to ~1e-10 would be possible.

Amplitude apodization of a telescope's pupil can be used to reduce the diffraction rings (Airy rings) in the PSF to allow high contrast imaging. Rather than achieving this apodization by selectively removing light at the edges of the pupil, we propose to produce the desired apodized pupil by redistributing the pupil's light. This lossless apodization concept can yield a high contrast PSF which allows the efficient detection of Earth-sized planets around stars at ~10pc with a 2m visible telescope in space. We review the current status of a JPL-funded study of this concept for the Terrestrial Planet Finder (TPF) mission, including a lab experiment and extensive computer simulations.

This paper summarizes our work designing optimal shaped pupils for high-contrast imaging. We show how any effective apodization can be created using shaped pupils and present a variety of both one-dimensional and azimuthally symmetric pupil shapes. Each pupil has its own performance advantage and we discuss the tradeoffs among various designs. Optimizations are typically performed by maximizing a measure of system throughput under constraints on contrast and inner working angle. We mention the question of sensitivity to aberrations. Controlling aberrations will be critical for any implementation of a planet-finding coronagraph. Finally, we present our first laboratory results testing a shaped pupil coronagraph.